Copper-beryllium alloys have been well known for many years as having excellent high strength characteristics. These alloys generally containing from 0.2 to 2.0% beryllium with optional additions of 1.0 to 3% nickel or cobalt are classified as precipitation hardenable copper-base alloys.
In precipitation hardenable copper-base alloys, one or more elements, which form a solid solution at elevated temperature but exhibit a decreasing solubility at lower temperatures, are alloyed with copper. The alloy is quenched from the solid solution region producing a supersaturated metastable phase and is subsequently thermally aged such that a second phase is precipitated out of the matrix. These precipitates act to block the motion of dislocations during deformation resulting in the observed strengthening. Further, due to the small amount of alloying elements, high conductivities in relation to strength as compared to traditional alloys can be obtained.
The resultant combination of properties of strength, ductility and conductivity are controlled by the amount, size and distribution of the precipitates. Therefore, the sequence and degree of work hardening and thermal aging which determine the kinetics of precipitation are critical in obtaining the desired properties.
Known processes for manufacturing wire from these copper alloys generally result in product having a tensile strength of 110 ksi and a conductivity of 48% IACS at the required elongation. Due to their superior strength, these alloys have found numerous applications in the connector industry. However, due to the relative low conductivity (pure copper is 100% IACS), conductor applications have been very limited. Further, fine stranded wires which would benefit most from the higher strength characteristics of these alloys cannot be easily processed due to the presence of extremely hard intermetallic precipitates.
Known processes for manufacturing wire from these alloys generally begin with the alloy in the desired precipitation hardened condition. The basic theory being that drawing to final size only acts to work harden the alloy and subsequent annealing will return the alloy to its original desired precipitation hardened condition. However, due to the presence of the extremely hard intermetallic precipitates in the precipitation hardened condition, excessive due wear occurs making wire drawing exceedingly difficult. Because of this, a flash plating of silver on the surface prior to drawing to reduce friction and/or intermediate stress relief anneals must be incorporated into the process to manufacture fine wire. This also limits the degree of cold working possible which significantly affects the final wire properties.
The instant invention provides for a method for manufacturing a fine wire product for signal and control wire applications. Wires manufactured with this process exhibit a surprising combination of tensile strength and electrical conductivity of at least 95 ksi and of 60% IACS respectively with at least 8% elongation in 10 inches. The instant invention further provides a method for efficiently manufacturing fine wires without the use of prior wire surface coatings (silver flash plating) or intermediate annealing treatments as essential processing steps to produce the final product.
U.S. Pat. No. 1,974,839 teaches the use of an alloy of 1-4% beryllium, 1.4-2.7% nickel and the remainder copper. The annealing range which is taught by this patent is from 200.degree. C. to 360.degree. C.
U.S. Pat. No. 2,172,639 discloses an alloy and a process for making an alloy with 24.6% conductivity and cold working of up to 60% reduction in area.
U.S. Pat. No. 3,663,311 discloses the processing of beryllium-copper alloys. None of the above prior art discloses a process for efficiently manufacturing a wire having the combination of strength, ductility and conductivity of the instant invention.